1. Field of the Invention
The present invention relates to a full-mesh optical wavelength division multiplexing transmission network transmission device for transmitting a plurality of optical signals wavelength-division multiplexed among a plurality of transmitting and receiving apparatuses.
This specification is based on Japanese Patent Application (No. 11(1999)-229174) to Japan Patent Office, and contents described in this Japanese Patent Application will be incorporated as a part of this specification.
2. Descriptions of the Related Art
An optical wavelength division multiplexinging (WDM) transmission system, which transmits a plurality of optical signals on one optical fiber by allocating the signals to different wavelengths, can increase significantly the capacity of its transmission path. In addition, the optical WDM transmission system can perform wavelength addressing which is capable of allocating the destination information relating to the optical signals to the respective wavelengths. Furthermore, a star-type WDM system, in which an Nxc3x97N wavelength multi/demultiplexer having a periodic wavelength demultiplexing property in input/output combination is arranged in the center so as to connect N transmitting and receiving apparatuses therebetween, can realize a full-mesh WDM transmission network device capable of interconnecting the apparatus through independent Nxc3x97N signal paths by using only N wavelengths optical signals.
FIG. 25 is a block diagram for explaining a schematic constitution of a conventional full-mesh WDM transmission network device. Referring to FIG. 25, reference numerals 1 to 4 denote transmitting and receiving apparatuses; 5 to 8, transmitters for sending WDM signals (wavelength xcexK:K=1, 2, . . . , N); 9 to 12, receivers for receiving the WDM signals (wavelength xcexK:K=1, 2, . . . , N); 13 to 16, 1xc3x97N wavelength multiplexers for multiplexing optical signals having different N wavelengths onto one optical fiber, 17 to 20, 1xc3x97N wavelength demultiplexing circuits for demultiplexing the WDM signals wavelength-multiplexed on one optical fiber, into signals having N wavelengths; 21, an Nxc3x97N wavelength multi/demultiplexer having a periodic wavelength demultiplexing property in input/output combination, which has a first I/O port group (1, 2, . . . , N on the left side) composed of N ports and the opposing second I/O port group (1, 2, . . . , N on the right side) composed of N ports; and 22 to 29, optical fibers for optically connecting the transmitting and receiving apparatuses 1 to 4, to the I/O ports of the Nxc3x97N wavelength multi/demultiplexer 21. In the optical fibers 22 to 29, the wavelengths xcexK (K=1, 2, . . . , N) of the WDM signals propagating on the optical fibers, the signals being wavelength-multiplexed, and the directions of the WDM signals to be transmitted, which are indicated by arrows, are shown.
In this prior art 1xc3x97N AWGs (arrayed-waveguide grating wavelength multi/demultiplexer) each having a first I/O port composed of one port and a second I/O port group composed of N ports facing the one first I/O port are used as the 1xc3x97N wavelength multiplexers 13 to 16 and the 1xc3x97N wavelength demultiplexing circuits 17 to 20. An Nxc3x97N AWG having a first I/O port group composed of N ports and a second I/O port group composed of N ports facing the first I/O port group and having a periodic wavelength demultiplexing property in input/output combination is used as the Nxc3x97N wavelength multi/demultiplexer 21.
FIG. 26 is a table showing a periodic wavelength demultiplexing property in input/output combination for Nxc3x97N AWG (N=8), and a port connection rule between the transmitting and receiving apparatus and the AWG in the conventional full-mesh WDM transmission network device. The Nxc3x97N AWG having the wavelength demultiplexing property of the periodic input/output relation can be realized by a method recorded in Japanese Patent Application No. 10(1998)-210679, and the like. The wavelength demultiplexing property between eight ports of the first input/output group of the Nxc3x97N AWG and eight ports of the second input/output group thereof is periodic as shown by the wavelength xcexK (K=1, 2, . . . , 8) in FIG. 26.
The Nxc3x97N AWG is a circuit symmetrical with respect to the first I/O port group and the second I/O port group. For example, the multiplexed WDM signal wavelength xcexK (K=1, 2, . . . , 8) input from a predetermined port of the first I/O port group is wavelength-demultiplexed and output to each port of the second I/O port group. In contrast, the multiplexed WDM signal wavelength xcexK (K=1, 2, . . . , 8) input from a predetermined port of the second I/O port group is wavelength-demultiplexed and output to each port of the first I/O port group.
The arrows shown above the each wavelength xcexK in FIG. 26 express the relation of the input/output among the ports. The arrows toward the right mean that the first I/O port group side is used as an input port and the second I/O port group side is used as an output port, and the arrows toward the left mean that second I/O port group side is used as an input port and the first I/O port group is used as an output port. To be more specific, in the conventional full-mesh WDM transmission network device, the whole of the first I/O port group side is used as the input port, and the whole of the second I/O port group side is used as the output port. Although there are 64 (8xc3x978) paths among 8xc3x978 AWG ports, the 64 paths can be independently established at only 8 wavelengths by using of the periodic wavelength demultiplexing property as shown in FIG, 26.
By connecting the I/O ports of the AWG to each transmitting and receiving apparatus, signals can be transmitted independently therebetween through all the paths which can be established among the eight transmitting and receiving apparatuses. Moreover, since a specified wavelength xcexK is allocated to the respective path, if a wavelength corresponding to a receiver is selected on the transmitter side, a wavelength addressing function to transmit the signal automatically to an objective receiver can be realized.
FIG. 27 is a diagram for explaining the wavelength addressing. In FIG. 27, reference numerals 31 to 38 denote eight transmitting and receiving apparatuses (1) to (8), and 39 denotes a 8xc3x978 AWG. The wavelength demultiplexing property of the 8xc3x978 AWG and the port connection rule between each of the transmitting and receiving apparatuses and the 8xc3x978 AWG are described in FIG. 26. An optical signal having a wavelength xcex2 transmitted from the transmitting and receiving apparatus (1) 31 is guided to the port 1 of the first I/O port group of the 8xc3x978 AWG 39, and switched within the 8xc3x978 AWG 39. The optical signal is then sent to the transmitting and receiving apparatus (2) 32 from the port 2 of the second I/O port group thereof. Similarly, a return signal xcex2 sent back from the transmitting and receiving apparatus (2) 32 is transmitted to the transmitting and receiving apparatus (1) 31 via the 8xc3x978 AWG 39. For example, optical signals xcex3 and xcex5 transmitted from the transmitting and receiving apparatus (1) 31 are automatically delivered to the transmitter (3) 33 and the transmitting and receiving apparatus (5) 35, respectively.
FIG. 28 is a graph showing atypical transmission spectrum property between certain input and output ports of the AWG fabricated as a silica-based planar lightwave circuit. Although a wavelength of an optical signal to be transmitted between the input and output ports is equal to xcexK, other than this optical signal also an optical signal (xcex1, xcex2, . . . , xcexKxe2x88x921, xcexK+1, . . . , xcexN) input from the same port can be scarcely transmitted therebetween. This is the noise called crosstalk light. An intensity ratio of the crosstalk light to the optical signal is approximately xe2x88x9230 dB with respect to a wavelength (xcexKxe2x88x921, xcexK+1) adjacent to the wavelength xcexK, and approximately xe2x88x9240 dB with respect to other wavelengths (xcex1, xcex2, . . . , xcexKxe2x88x922, xcexK+2, . . . , xcexN).
In the Nxc3x97N AWG of the conventional full-mesh WDM transmission network device, the WDM signals of N wavelengths are input from all ports of the first I/O port group. For example, in the case of the 8xc3x978 AWG having the wavelength demultiplexing property of the periodic input/output relation as shown in FIG. 26, the optical signal xcex5 (thick solid line) which is transmitted from the transmitting and receiving apparatus (1) 31 and input to the 8xc3x978 AWG via the port 1 of the first I/O port group (the port group on the left side of the 8xc3x978 AWG) is output from the port 5 of the second I/O port group (the port group on the right side of the 8xc3x978 AWG), and received by the transmitting and receiving apparatus (5) 35.
Furthermore, the optical signal xcex6 (thick broken line) which is transmitted from the transmitting and receiving apparatus (2) 32 and input to the 8xc3x978 AWG via the port 2 of the first I/O port group is output from the port 5 of the second I/O port group, and received by the transmitting and receiving apparatus (5) 35. At this time, crosstalk light (thin solid line) of the optical signal xcex5, which is transmitted from the transmitting and receiving apparatus (2) 32 and input via the port 2 of the first I/O port group, is also output from the port 5 of the second input/output group. Similarly, crosstalk lights of the optical signal xcex5 transmitted from other transmitting and receiving apparatuses are also output from the port 5 of the second I/O port group. As a result, one optical signal xcex5 and seven crosstalk lights having the equal wavelength are output from the port 5 of the second I/O port group. The crosstalk lights having equal wavelengths are called coherent crosstalk lights. At this time, since the coherent crosstalk lights from the port 2 and the port 8 of the first I/O port group, that is, the ports cyclically adjacent to the port to which the optical signal xcex5is input, are crosstalk light from the adjacent wavelength (adjacent crosstalk light), these coherent crosstalk lights show intensities stronger than those of other five coherent lights.
Like the Nxc3x97N AWG in the conventional full-mesh WDM transmission network device, when N optical signals having the equal wavelength are input from the same I/O port group side, Nxe2x88x921 coherent crosstalk lights always occur. Moreover, since the coherent crosstalk light is the noise having a wavelength equal to that of the optical signal, the optical signal and the noise cannot be separated from each other by a wavelength demultiplexing circuit of the transmitting and receiving apparatus, and the noise may increase owing to the interference of the plurality of coherent crosstalk lights.
In the conventional full-mesh WDM transmission network device, a certain WDM wavelength light received by the transmitting and receiving apparatus is a sum of one optical signal and Nxe2x88x921 coherent crosstalk lights, and two waves among these waves are the adjacent crosstalk lights. If the optical signal has the longest wavelength xcexN or the shortest wavelength xcex1, one wavelength is the adjacent crosstalk light. Accordingly, a signal noise ratio S/N is expressed as follows:
S/N=PSignal/[2PAdjCT+(Nxe2x88x923)PothCT]xe2x80x83xe2x80x83(1)
where PAdjCT, POthCT and PSignal are the adjacent crosstalk light intensity, the non-adjacent crosstalk light intensity and the signal light intensity. Assuming that PAdjCT/PSignal is equal to xe2x88x9230 dB and POthCT/PSignal is equal to xe2x88x9240 dB, S/N is 27 dB when N=4, 26 dB when N=8, and 25 dB when N=16.
As taught by the formula (1), in the conventional full-mesh WDM transmission network device noises created by the coherent crosstalk lights are accumulated with an increase in the number N of the transmitting and receiving apparatuses connected, so that S/N of the WDM wavelength light decreases. This implies that communication quality of the system deteriorates along with scale expansion. In contrast, a system satisfying a predetermined communication quality standard is limited in its scale. This is a serious problem in designing the system.
The present invention was made in view of such problems, and the object of the present invention is to provide a large scale full-mesh optical wavelength division multiplexing transmission network device which reduces the accumulation number of coherent crosstalk lights that cause noise, and has a communication quality more excellent than the conventional full-mesh optical wavelength division multiplexing transmission network device, without any modification of constituent components constituting the conventional one. The constituent components include a transmitter, a receiver, a 1xc3x97N wavelength multi/demultiplexer, an Nxc3x97N wavelength multi/demultiplexer, and an optical fiber.
The full-mesh optical wavelength division multiplexing transmission network device of the present invention comprises N transmitting and receiving apparatuses; and an Nxc3x97N wavelength multi/demultiplexer having a first I/O port group composed of N ports connected to a different one of said N transmitting and receiving apparatuses and a second I/O port group composed of N ports connected to a different one of said N transmitting and receiving apparatuses, wherein an optical signal having a different wavelength for each port of the second I/O port group among optical signals having N kinds of wavelength is transmitted between any one of the ports of the first I/O port group and each port of the second I/O port group; an optical signal having a different wavelength for each port of the first I/O port group among optical signals having N kinds of wavelength is transmitted between any one of the ports of the second I/O port group and each port of the first I/O port group; as a result, N port combinations for transmitting optical signals having an equal wavelength exist for each wavelength, among Nxc3x97N port combinations made by the N ports of the first I/O port group and the N ports of the second I/O ports; among the N port combinations for transmitting the optical signals having the equal wavelength, in M port combinations the optical signals are transmitted from the first I/O port group to the second I/O port group, and in Nxe2x88x92M port combinations the optical signals are transmitted from the second I/O port group to the first I/O port group; and the port of the second I/O port group for receiving the optical signal from the port of the first I/O port group connected to the any one of the transmitting and receiving apparatuses and the port of the first I/O port group for receiving the optical signal from the port of the second I/O port group connected to the any one of the transmitting and receiving apparatuses are connected to the different transmitting and receiving apparatus.
In the optical wavelength division multiplexing transmission network device of the invention, N is preferably an even number and M is equal to N/2.
In the optical wavelength division multiplexing transmission network device of the invention, wavelengths of all optical signals transmitted from any one of the ports of one I/O port group to the other I/O port group are preferably different from wavelengths of all optical signals transmitted from a port adjacent to the said one port of the one I/O port group to the other I/O port group.
In the optical wavelength division multiplexing transmission network device of the invention, the transmitting and receiving apparatus preferably further includes: Nxe2x88x92M transmitters; M receivers; a 1xc3x97N wavelength multi-demultiplexer which demultiplexes an optical signal output from predetermined one port of the first I/O port group into M optical signals having different wavelengths, inputs the demultiplexed optical signals to the different receivers among the M receivers, multiplexes optical signals output from said Nxe2x88x92M transmitters into one optical signal, and transmits the multiplexed optical signal to predetermined one port of the first I/O port group; M transmitters, Nxe2x88x92M receivers; and a 1xc3x97N wavelength multi/demultiplexer which demultiplexes an optical signal output from predetermined one port of the second I/O port group into Nxe2x88x92M optical signals having different wavelengths, inputs the demultiplexed optical signals to the different receivers among the Nxe2x88x92M receivers, multiplexes optical signals output by said M transmitters into one optical signal, and transmits the multiplexed optical signal to predetermined one port of the first I/O port group.
According to the present invention, a full-mesh optical wavelength division multiplexing transmission network device can be realized, which is capable of reducing the accumulation number of coherent crosstalk lights that cause noise, exhibiting excellent communication quality, and being mass produced, without any modification of constituent components (the transmitters, the receivers the 1xc3x97N AWG, the Nxc3x97N AWG and the optical fiber) constituting the conventional one.